Epoxy thiolactones as a platform for polyurethanes

Epoxy thiolactone coupling agent for multicomponent reactions or for the synthesis of polymeric architectures.

Using an epoxy thiolactone coupling agent, DWI researchers established a versatile toolbox to allow synthesis of poly(thioether urethane)s with various architectures. The epoxy thiolactone system can either help to connect different building blocks, create polymer chains in a polyaddition process or form bulk hydrogels in combination with other low-molecular weight building blocks in a multicomponent reaction.

The key feature of this coupling agent is that its different cyclic components allow an orthogonal reactivity towards amines. This way, a single reaction trajectory can be pursued in opening the thiolactone ring, which is derived from homocysteine thiolactone – a biobased component. Upon ring-opening of this thiolactone and attachment of a functional amine a thiol is released. This thiol is susceptible to one of the manifold thiol-X reactions (e.g. thiol-ene Michael addition). As a third functionality, the epoxide is transformed using a secondary amine at elevated temperatures. Finally, the excellent regioselectivity of this coupler allows to combine three different molecules in a one-pot multicomponent reaction. If the thiolactone ring is opened without trapping the resulting thiol group, a base-catalyzed thiol-epoxy addition can occur. The free thiol is added to the epoxy ring in a nucleophilic fashion forming a β-hydroxy thioether bond. Here, the used amine is incorporated into the side chain of the resulting polymer. This thiol-epoxy polymerization is carried out at mild conditions to deliver functional poly(thioether urethane)s. The final strategy uses this coupling agent for the preparation of hydrogels. If a diamine is used in combination with a diacrylate, a multicomponent reaction is triggered which drives the different molecules to build up a dense network and, ultimately, to form hydrogels. These hydrogels host intact epoxides, which can be used for subsequent functionalization of the gels.